Implantable drug delivery devices are commonly used to provide site specific and/or sustained delivery of beneficial agents to address adverse patient conditions. The pumps are used for the continuous medication delivery over relatively long periods of time in patients who could otherwise only be treated by injecting the medications, such as, e.g., morphines, heparins and similar drugs, several times daily. Pumps are advantageous in comparison with injections in that an even flow rate and a significantly lower total intake of the drug can be realized.
Implantable drug pumps typically include a reservoir for storing a fluid, such as a drug, and a pump or other flow control device to deliver the fluid to a site within a patient. A septum is formed on the top of the pump to allow refilling of the reservoir. Most implantable pumps also include a bolus port which is coupled to the catheter to enable a one-time injection directly to the treatment site. In use, the pump is disposed in a subcutaneous pocket in the area of the abdomen of the patient whereby the refill opening sealed by the septum is palpable under the skin of the patient. The medication reservoir is filled by piercing the skin of the patient and the septum with the corresponding needle of a syringe.
During treatment for certain medical conditions, the amount of medication being delivered from the pump may need to be adjusted. Accordingly, variable flow rate programmable pumps have been developed that allow the flow rate to be adjusted over time. These pumps typically include a battery as an energy source that is used to open and close a valve to adjust the flow rate. While these pumps provide some advantages over fixed flow rate pumps, the use of such pumps has some drawbacks. In particular, variable flow rate pumps have a normal life that is limited by the life of the battery. Since these pumps require an active pumping mechanism or an active valve to control flow rate, the pumps tend to be inefficient as they consume energy to operate the pump. After that, removal of the pump is necessary in order to renew the energy source. Further, in order to guard against the shortening of the device's useful life, variable flow rate pumps are typically not manufactured with additional power-consuming features such as sensors and other diagnostic equipment which would provide useful for monitoring the patient during treatment. One other problem associated with current variable flow rate pumps is that they only allow for a limited number of pre-set flow rates.
Accordingly, there remains a need for an implantable pump having an adjustable flow rate, and that has an extended useful life.